When was my Grandfather born?

My grandfather’s obituary listed both 1887 and 1889 as his year of birth. His World War I registration card (part 1, part 2) shows 1890. His World War II registration card (part 1, part 2) also shows 1890. His marriage certificate notes that he was 29 in 1920. Because he was married on January 29 he would have turned 30 on his birthday on March 29. 30 years before 1920 is 1890.

On the other hand, according to my sister, the family bible, his death certificate, and the estate tax forms filled out after his death show 1889.

We know that people would often fudge their age to join the military or to get married; but in this case those reasons don’t apply. One year’s difference wouldn’t have affected either his military or marriage eligibility.

There is no clear weight of evidence to decide in favor of either 1889, 1890, or 1891 so this will have to remain a mystery.